Yeah every 360 game has a couple of hundred points worth of "cheese" achievements which require nothing more than completing a game on the normal setting. But most games have lots of achievements are either extremely difficult to obtain, extremely time consuming. The only game in which I have gotten every achievement in is oblivion (including the shivering isles expansion ones). It took me about 150 hours to do all that.
What games have you done it in and how many hours did it take you (if the game has a time log).